


Of sound minds

by Askellie



Category: Undertale (Video Game)
Genre: Blood and Gore, Body Horror, Captivity, Fontcest, Infection, Insanity, Isolation, M/M, Medical Experimentation, Non-Consensual Body Modification, Obsession, Possession, Psychological Torture, Quadruple amputation, Rape/Non-con Elements, Sibling Incest, Torture
Language: English
Status: Completed
Published: 2021-01-14
Updated: 2021-01-14
Packaged: 2021-03-12 08:36:25
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 1
Words: 3,430
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28757463
Author URL: https://archiveofourown.org/users/Askellie/pseuds/Askellie
Summary: Gaster is the former Royal Scientist, the savior of the Underground, and Papyrus is his chosen successor. Papyrus thought it strange at first, but the longer Gaster lives in his soul the more Papyrus understands why he was chosen. They’re so alike, he and Gaster. They’re smart and brave and clever. They only want the best for monsterkind.And for Sans.
Relationships: Papyrus/Sans (Undertale)
Comments: 4
Kudos: 38





	Of sound minds

**Author's Note:**

> This fic was written for the amazing Undertale Zine [Lattices & Cracks](https://lattices-and-cracks.itch.io/fanzine), which is an epic and beautifully illustrated FREE downloadable zine themed around skeleton-centric gore. I highly recommend downloading the zine so you can see the accompanying art that was done for this fic by the incredible [Denko](https://twitter.com/DunkingNuts). Make sure you read all the warnings! This fic is very dark, as is the zine itself if you choose to read it.
> 
> You can download the zine [here](https://lattices-and-cracks.itch.io/).

“How does it feel, Sans?” Papyrus asks brightly, yanking firmly on the leather strap until he hears Sans’s carpals grind unforgivingly against the examination table. “Comfortable?”

“Uh…” There’s a sheen of sweat on Sans’s skull. His eyelights have almost vanished in the horrified pits of his sockets. “Not really, bro. You wanna maybe untie me? I really think we should talk.”

“Don’t be silly,” Papyrus scoffs. Now that he’s satisfied Sans won’t be able to free himself, it’s time to collect his tools. He’s never been in the lab before, but Gaster’s voice murmurs precise instructions to let him know exactly which cabinets to open. The gleaming array of neatly organised implements is an absolute delight to behold. Papyrus chooses with care, arranging each on a tray like one might prepare a nutritious meal.

“I’m quite sure that every word you have to say to me is a lie. Besides, there’s important work to be done! Like…”

He trails off, hands hovering over a selection of filled syringes. What was he doing again? It’s an immense challenge, trying to stay focused with all the new thoughts and memories filling his skull. It’s like trying to navigate through a familiar house in pitch darkness when someone has deviously rearranged all the furniture.

_ We’re taking care of Sans _ , Gaster reminds him. His voice is calm, authoritative: a constant source of helpful suggestions. He tells Papyrus all sorts of useful things, like the entrance code to the lab and how to squeeze Sans’s soul with blue magic until he passes out.

Papyrus never understood before how Sans could gush over his silly physics books and magazines full of pictures of the stars, but now he knows. Science is wonderful. There’s so many amazing things he never knew, so many exciting ideas he wants to try.

There’s a furtive shuffle of movement behind him. Papyrus turns to look over his shoulder to find Sans freezing in the process of swivelling his wrists and trying to find some measure of leniency against his restraints.

The smirk that pulls at Papyrus’s mouth feels unfamiliar and strange, as is his tone when he cooly offers, “I’m afraid you’ll find I’ve taken thorough precautions, Sans. I’m sure you’ve noticed the magic blocker’s effectiveness against your shortcuts, but I really do advise against struggling too much. I wouldn’t want you to hurt yourself.”

Sans’s face twists through a complicated series of emotions, passing through shock and grief before finally settling on anger. “You’re… Gaster?”

“Oh yes,” Papyrus says tightly. “I’m quite upset that you never told me about him.”

Gaster is the former Royal Scientist, the savior of the Underground, and Papyrus is his chosen successor. Papyrus thought it strange at first, but the longer Gaster lives in his soul the more Papyrus understands why he was chosen. They’re so alike, he and Gaster. They’re smart and brave and clever. They only want the best for monsterkind.

And for Sans.

Sans looks conflicted, his scowl softening with guilt. “Bro…”

“But that’s in the past,” Papyrus continues with benevolent ease, carrying his tray of beautiful, shining implements back to the table. “Right now, this is about you, Sans. Everything I’m doing is for you.”

“Pap, please,” Sans pleads. His face is so open and earnest, his lying grin finally discarded. “We can-hrk!”

One of the first gifts Gaster gave him was the use of his floating hands. Such useful constructs; he directs two of them to hook into the corners of Sans’s mouth and pry it open. A third one slides between his helplessly parted teeth and curls down behind his jawbone. The cyan blue of his magic forms by reflex, creating a tongue that the construct pinches tightly between its fingers so it can be dragged into the open. Sans chokes, sockets watering at what must be an uncomfortable strain where the magic is rooted inside his skull. 

“This is a magic stabiliser,” he tells Sans, lifting the syringe into view, priming it with a gentle squeeze. “Your low HP adds challenge to the procedure, but this will help ensure you can withstand some damage without dusting. I understand you may be tempted to pass out from the pain, but the results will improve if you remain conscious so please do your best.”

Sans can’t reply, only gag weakly around the constructs’ invading fingers as the drug is injected into his conjured magic. 

* * *

Sans’s face is a beautiful mess, streaked with the sticky residue of his tears and mottled with dark patches of sweat. It’s an enthralling contrast to the way his expression is completely lax, eyes softly shuttered, his jaw gone slack and his mouth slightly askew. Papyrus can’t stop touching him, marvelling at the delicate contours of Sans’s round features. He paints a masterpiece of agony and filth with Sans’s fluids, his fingertips leaving smeared brands across Sans’s skull.

He’s just adding the finishing touches when Sans comes awake violently, his left eye strobing with lightning flashes of yellow and cyan as he convulses against the straps. He makes a ragged sound like the dying keen of an animal until his strength abruptly gives out and leaves him pliant and gasping. His gaze darts wildly back and forth before settling on Papyrus’s face.

“Pap…” For one moment, he looks relieved, like all the times Papyrus was there to wake him after a nightmare. Then the pain hits. The frantic fit of hyperventilating panic makes his bones rattle so hard Papyrus wonders if he’ll break himself apart.

“Hush, brother. It’s okay! You did it. I’m so very, very proud of you!” Papyrus runs his hand over Sans’s skull, soothing him until his uncontrollable seizing subsides into quiet shudders. When his unevenly blown eyelights finally land on the results of Papyrus’s hard labour, he stops moving all together.

“Do you like it?” Papyrus asks with a jubilant smile. “I was a little worried since it was my first attempt, but the cuts are very clean!”

He’d been dissatisfied with how heavy and clumsy the tools felt in his hands, but Gaster’s warm voice assures him he’s done a masterful job. Each of Sans’s carpals have been cleaved in half, all the distal phalanges entirely removed. The bloody stumps have been carefully bandaged, dark spots of marrow blotting at the tips where Sans’s fingers used to be.

“Next time I think we can go as high as your wrist,” Papyrus informs him eagerly. He traces an exploratory line across the bottom of Sans’s radius and ulna, imagining the beautiful honeycomb of marrow inside the bone. “As long as we don’t take too much, your HP only drops a little! Isn’t that fascinating, Sans?”

Sans can’t seem to articulate anything more than a whimper, staring at Papyrus in stifled horror. His mouth is trembling ever so slightly. It makes Papyrus think of how easily he could lean down and kiss Sans to taste the sharp tang of pain and terror on his tongue.

Gaster thwarts his temptation, reminding him that Sans isn’t ready for him (them) yet. It’ll be even sweeter if he waits. More perfect. He doesn’t want Sans as a numb, shell-shocked husk unable to react. He wants Sans to beg for his kindness, for mercy, for the love Papyrus has been holding back so long for reasons that seem utterly silly now.

He’s going to make Sans his (theirs), one small piece at a time. He (they) can’t wait.

* * *

Papyrus scrubs his hands mechanically in the sink, grinding his phalanges together for the requisite thirty seconds of sterilisation before reaching for a fresh pair of gloves. In the steel cabinet above the counter he catches a distorted glimpse of his reflection and the fresh, dark crack trailing from his socket. The wave of fury is so intense he almost feels light-headed; he sways on his feet before mastering himself again.

He tears the first pair of gloves when he pulls them on, the latex snapping with a crack of sound. Papyrus snarls and throws them aside, donning another set with more care.

“That was very unkind, Sans,” he says, precisely enunciating every syllable so the tone of his anger doesn’t bleed into his voice. “I don’t like to consider it, but sometimes I feel like you’re a terrible brother.”

Clearly he’s been too lenient. He’d grown used to Sans’s dispirited lack of resistance. When Sans meekly asked if Papyrus could loosen the strap on his remaining wrist to ease the raw and bloody chafing beneath, Papyrus had agreed, wanting to reward him for his good behavior.

Papyrus doubts Sans has ever thrown a punch in his life, which is why he never thought to expect it. Sans’s small fist had caught Papyrus in the face right where the bone was thin and brittle, causing a jagged split from his eye down his cheekbone. It’s a distressing mirror of the scar Gaster once possessed, and an unsightly blemish that doesn’t belong on someone as great as Papyrus.

_ An unfortunate mistake _ , Gaster observes bluntly.  _ You’re still too soft. Perhaps I was wrong about you…? _

“Be quiet,” Papyrus says sharply. He isn’t speaking to Sans, but the muffled ruckus across the room tapers to a breathless sob. Papyrus takes a steadying breath and extracts the bonesaw from the stack of unwashed implements beside the sink. There’s still flaking blood and dust on the blade. He turns around and appreciates the fresh rush of terror in Sans’s eyes.

“I wasn’t going to do this yet, Sans, but you haven’t left me with much choice,” Papyrus says. He can’t quite manage to sound contrite -- he’s too upset for that -- but a small part of him does regret that he won’t get to appreciate the same long, slow deconstruction process he enjoyed with the first limb.

Sans has proven he can’t be trusted with his arms, so he doesn’t get to keep them.

Before attending to his newly fractured face, Papyrus made sure Sans was thoroughly tied down again, calling on Gaster’s constructs for assistance. They’re swarmed on Sans like flies on a fresh corpse, pinching and tugging on both the restraints and his bones to make sure there’s no leeway for further assaults. The straps have all been mercilessly tightened to the point that he can see blood seeping out where Sans’s radius has snapped from the strain. Two fingers are broken as well; the untimely punch hurt Sans just as much as it did Papyrus.

One of the punctured hands has its long, spidery fingers hooked into Sans’s eye-sockets, holding them open so he can’t block out his imminent punishment. A rubber gag keeps his pleading constrained behind his teeth, though it doesn’t stop him from trying. Saliva is running desperately down his chin as he huffs and gurgles with inarticulate urgency.

Sans does indeed look very sorry for his actions, but as Papyrus already knows, Sans is an excellent liar.

Just a few hours earlier, Papyrus had finally trimmed Sans’s right arm to what he and Gaster agree is the ideal length. The final cut leaves Sans with precisely six remaining inches of his humerus intact. Papyrus sketches out a matching line on Sans’s left arm with a black marker, cursing under his breath when Sans’s quivering makes the ink stutter.

“Don’t move unless you want this to turn out crooked,” he scolds, smearing away his first attempt to try again. He can’t stand a poorly done job, and if he has to take another inch off each arm to keep things even and precise, he will. Once he’s satisfied his line is perfectly straight, Papyrus reaches for the saw again and sets its grimy teeth against Sans’s humerus. He stares right into his brother’s tear-filled sockets.

“It’s okay, Sans,” he says, because unlike Sans, he’s a good brother. He can be kind, even if he’s angry, and above all he’s certainly still  _ worthy _ no matter what Gaster thinks. “I still believe in you.”

The first stroke of the saw makes Sans screech incoherently into the gag. Though there should be enough of the magic stabiliser left in Sans’s body to keep his HP from dropping, all of its pain-diminishing properties will have faded by now. The sound almost seems too loud to have come from such a small, crippled body. Sans’s broken fingers scrabble mindlessly against the table, and his sockets go dark, open but sightless.

Papyrus draws the saw back for its second pass. Its saw’s blade cracks through the outer subcutaneous layer of bone and breaches the vessels of the marrow. Bright red blood spills onto the table in an unexpected rush. Gaster idly notes that Sans must be incredibly adrenalised for his circulation to be working so hard.

However, Papyrus is pleased to note that Sans’s HP has only dropped a fraction of a point. His intent is perfectly restrained despite his temper. The movement of his arm is steady, back and forth, carving through the bone with absolute precision despite how desperately Sans is writhing beneath him. The saw’s rhythm feels soothing. Papyrus can almost lose himself in it as Sans’s wordless howls of agony start to diminish and his convulsing body goes slack.

He’s almost finished, the bone held on by only a splintered fragment before he realises that Sans’s face has turned chalky and grey. He’s no longer moving. There is an awful lot of blood on the table.

“Oh,” he gasps, dropping the saw. Normally he would also be using the heated blade of a scalpel to cauterise the wound as he went, but in his distraction he had simply forgotten. For a moment he can’t move, numbed by panic and an even more paralysing fascination. Sans’s blood is thick and rich, a swirling pool of glorious crimson. He makes a note to gather it all up afterwards for careful preservation in a jar along with the other pieces of Sans’s body before he rushes to drag his beloved brother back from the brink of dusting.

* * *

The open wound and the unfortunate choice of dirty tools mean that Sans’s body is ripe for the onset of infection. For the next week he burns hot with fever. His bones shed a fine layer of dust. His marrow turns dark and sour, filling the lab with the rancid stench of sickness.

Sans no longer needs restraining. He’s rarely conscious, and even more infrequently lucid. He can barely be coaxed into eating or drinking, so Papyrus is forced to keep him on a steady IV drip. The need for constant supervision means Papyrus has taken Sans from the main laboratory and brought his brother into the small, unadorned breakroom he’d claimed for himself.

The rooms upstairs are larger -- and empty now that Papyrus has removed the false Royal Scientist from her unearned title -- but it’s easier to stay entirely in the restricted levels of the lab. No one knows he’s here. He can continue his work undisturbed until Gaster deems him ready to announce their existence to the King.

Despite the breakroom’s size, its bed is unexpectedly wide and well-appointed. It could easily fit them both, but Papyrus often chooses not to sleep. He stays awake to watch over Sans, attentively wiping the sweat from his body, changing his bandages and topping up the cocktail of antibiotics in the IV. Sometimes, when Sans is moaning and mumbling in his sleep, Papyrus even administers a sedative to help him rest.

(He’s a good brother, Gaster assures him. It’s not like Sans was happy before. Only Papyrus can fix that, make him appreciate what he has.)

Sans remains weak and listless even when the dangerous fever wanes. He lies plainly in Papyrus lap, absorbing his brother’s relentlessly upbeat chatter without attempting to interrupt or respond. He doesn’t react when Papyrus’s hands wander in both clinical examination of his condition and sometimes just for his own gratification. Papyrus’s hands are nearly large enough to span the height of Sans’s ribcage; he likes the click his fingers make as he drags them back and forth over the intercostal spaces.

The matching stumps of Sans’s arms require especially delicate handling. At first, Sans flinches reflexively at any pressure even as far up as his shoulder, but repeated contact starts to desensitise the inflamed bone. Papyrus repeats the act daily, each time allowing his fingertips to delve lower, circling down to the blunt, stunted tips. Even when he’s not thinking about it, his hands have a tendency to return there, marveling at the clean severance of bone.

It’s during one such exploration that Sans gives a surprised, sharp inhale in response to a careless squeeze. Papyrus stops immediately, worried he may have damaged Sans’s tenuous compliance, but instead of trying to pull away Sans only gives his stump a small wiggle, wordlessly encouraging Papyrus to continue.

“Did you like that, Sans?” he asks earnestly, trying not to let his body strum like a plucked guitar string in hopeful anticipation. He does it again, just in case Sans needs to be convinced, cupping the helpless limb in the broad span of his palm. Sans’s breath stutters.

“Yes.” Sans’s voice is a dead, dry rasp, but Papyrus is overjoyed.

“Oh, Sans,” Papyrus breathes, holding his brother’s frail body to his chest, tightly but oh so carefully. Sans is still sick; he needs to be gentle. “I’m sorry I called you a bad brother. I love you.”

Sans doesn’t reply at first. Papyrus almost thinks he may have fallen asleep again, the lazy bones, but after several long, pregnant seconds Sans brokenly whispers, “Love you, Pap.”

They’re the words Papyrus has been waiting weeks (months, years) to hear. He could almost cry, he’s so happy. Sans must be too; there are tears of relief dripping from his sockets. Papyrus nuzzles him affectionately, licking them away and pledging his adoration and devotion over and over again as Sans unresistingly spends the night in his arms.

* * *

Over time, Papyrus adds personal touches to make the room more habitable now that he and Sans are sharing it. He puts up paintings of the outside world that Sans is no longer allowed to see. He refurbishes the bed with nicer sheets and comfier pillows and a sturdy headboard strung with chains that have been specially crafted for Sans’s modified limbs. Sans rarely misbehaves anymore, which is almost a disappointment. Sometimes Papyrus will have to invent some trivial slight deserving of punishment just so he can string Sans up and listen to him cry and beg for forgiveness.

Sans spends most of the time sleeping and rarely leaves the bed. It would be difficult for him to even attempt it now that Papyrus has completed the procedures to remove his legs, leaving him with shortened femurs only slightly longer than his humeri. It’s quite entertaining to watch him move around, carefully balancing on his tender stumps. The disparate height in his limbs means his hips are always more elevated than his skull, his pelvis jutting and tailbone lifted like an obscene invitation. He’s as clumsy as a newborn kitten, and just as endearing.

Whenever Papyrus has to leave -- for supplies, for the ongoing experiments he’s begun in the labs under Gaster’s rigorous guidance -- he knows Sans misses him. Sometimes he stays away longer than he should and watches through the cameras as Sans’s loneliness turns to terror, until he’s screaming Papyrus’s name and begging him to come back, pleading not to be left alone in his tiny, windowless prison.

Regardless of how long or short his absence, Sans is always desperately relieved to see him. The magic in his pelvis will be formed and waiting, ready for Papyrus to give him the little bit of stimulation he needs to help his pussy form. Sans can’t touch himself, and often Papyrus is simply too impatient to administer much in the way of foreplay. Sans still wails and sobs frequently when he’s penetrated, his dry passage agonisingly stretched out by the merciless entry of his brother’s cock. Papyrus loves the way every time feels like their first. With Sans’s magic being conjured anew for each session he’ll never have the chance to adapt to Papyrus’s formidable length and girth.

Sometimes, though, the burn of friction is more painful than stimulating even for Papyrus, and more and more he starts to think over Gaster’s helpful suggestions about further ways they could improve Sans’s body for their enjoyment. His brother is everything he’s ever wanted, but the idea that he could be even more so… well, perhaps that can be explored in another experiment.

  
  
  



End file.
